Mahan excitons in room-temperature methylammonium lead bromide perovskites

Tania Palmieri, Edoardo Baldini (), Alexander Steinhoff, Ana Akrap, Márton Kollár, Endre Horváth, László Forró, Frank Jahnke and Majed Chergui ()
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Tania Palmieri: Institute of Chemistry and Chemical Engineering (ISIC), École Polytechnique Fédérale de Lausanne (EPFL)
Edoardo Baldini: Institute of Chemistry and Chemical Engineering (ISIC), École Polytechnique Fédérale de Lausanne (EPFL)
Alexander Steinhoff: Institute for Theoretical Physics, University of Bremen
Ana Akrap: Université de Fribourg
Márton Kollár: Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL)
Endre Horváth: Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL)
László Forró: Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL)
Frank Jahnke: Institute for Theoretical Physics, University of Bremen
Majed Chergui: Institute of Chemistry and Chemical Engineering (ISIC), École Polytechnique Fédérale de Lausanne (EPFL)

Nature Communications, 2020, vol. 11, issue 1, 1-8

Abstract: Abstract In a seminal paper, Mahan predicted that excitonic bound states can still exist in a semiconductor at electron-hole densities above the insulator-to-metal Mott transition. However, no clear evidence for this exotic quasiparticle, dubbed Mahan exciton, exists to date at room temperature. In this work, we combine ultrafast broadband optical spectroscopy and advanced many-body calculations to reveal that organic-inorganic lead-bromide perovskites host Mahan excitons at room temperature. Persistence of the Wannier exciton peak and the enhancement of the above-bandgap absorption are observed at all achievable photoexcitation densities, well above the Mott density. This is supported by the solution of the semiconductor Bloch equations, which confirms that no sharp transition between the insulating and conductive phase occurs. Our results demonstrate the robustness of the bound states in a regime where exciton dissociation is otherwise expected, and offer promising perspectives in fundamental physics and in room-temperature applications involving high densities of charge carriers.

Date: 2020
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DOI: 10.1038/s41467-020-14683-5

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